This invention relates to an apparatus for filtering a liquid wherein filtration is effected by tangential flow of the liquid across a filter surface. More particularly, this invention relates to such a filtration apparatus wherein a plurality of filters are arranged in a stacked relationship and secured to a manifold which permits introduction of the liquid and removal of rentate and filtrate.
Prior to the present invention, liquids, primarily aqueous liquids have been filtered by tangential flow devices wherein a plurality of filters are stacked between two manifolds, one at the bottom of the stack and one at the top of the stack. The filters are separated by appropriate screens and liquid impervious layers to permit liquid flow, as well as filtrate and retentate flow into and from the stack. In addition, flow holes are provided through the layers within the stack. The holes are sealed appropriately to prevent admixture of filtrate with incoming liquid or retentate. The manifolds are designed so that filtrate is removed from both the top and bottom manifolds while incoming liquid is introduced into one manifold and retentate is removed from the second manifold. This manifold arrangement necessitates fittings to both manifolds in order to supply and remove liquid to and from the stacks. This is undesirable since additional manipulative steps for removing and connecting the fittings are required when it is desirable to replace the filtration elements forming the stack. In addition, the use of two manifolds to remove filtrate from the stack undesirably increases the filtrate volume retained within the stack. Furthermore, the requirement of two manifolds is undesirably expensive.
Accordingly, it would be desirable to provide a tangential flow filtration apparatus which utilizes only one manifold and which prevents admixture of liquid to be filtered, filtrate and retentate.